Rock Physics And Seismic Response Research Of Partial Gas-saturated Sandstone Reservoir

Gas saturation is a critical parameter which determines whether the reservoir has a commercical ecploitation value in both conventional high-porosity sand reservoir and tight gas sand reservoir.As the tight gas sand reservoir has become the importmant area in seismic exploration and development of unconventional reservoir,the identification of highly gas-saturated reservoir is the key target in seismic exploration,therefore it is significant to develop the research around quantitative prediction of gas saturation.In this paper,the influence of single parameter on the elastic modulus of sandstone is studied by controlled parameter artificial sandstone method,which provides theoretical support for AVO forward and inversion.By using AVO mathematic forward method,the effect of the sandstone mineral,clay content,gas-water mixture saturation pattern and reservoir thickness on the AVO characteristics are analyzed.A physical model of sandstone with different gas saturation is constructed by combining the rock physical analysis and physical simulation.The gas-saturation of conventional high-porosity and tight gas sandstone reservoir is predicted by using AVO characteristic and pre stack simultaneous inversion methods after data acquisition and processing.In the aspect of rock physics,the effect of single parameter on the elastic parameters of sandstone is studied.The influence of skeleton mineral,clay content,water saturation and pressure on the elastic modulus of sandstone is researched experimentally and theoretically by aitificial sandstones,natural sandstone samples and well logs.The improved Xu-White model can predict the elastic parameters of the sandstone more accurately,which provides a theoretical support for the AVO forward modeling and pre stack inversion.In the AVO characteristic analysis,mathematical forward is used to analyze the changes of the AVO response and attribute when four important parameters are changedrespectively,which are framework mineral,clay content,gas-water saturation pattern and reservoir thickness.The results show that AVO response changes almost linear with mineral and clay content,the gas-water saturation pattern has an important influence on the AVO characteristics of different gas-saturated sand,while the reservoir thickness may have an interference effect on AVO characteristics.In the gas-saturation quantitative prediction,based on the combination of rock physical analysis and seismic physical modeling,a seismic physical model of different gas-saturation sandstone reservoir is constructed,and the predictive ability of gas-saturation in conventional high-porosity sandstone reservoir and tight gas sand reservoir is compared by using AVO characteristic and pre stack simutaneous inversion methods.The results show that the AVO characteristic can predict gas-saturation in tight gas sand reservoir semi-quantitativly,but it is weak for conventional sandstone reservoir.By using the pre stack simultaneous inversion method,the quantitative prediction of gas-saturation in two kinds of gas bearing sandstone reservoirs can be obtained by using different sensitive parameters in the optimized inversion results respectively.